I. Field of the Invention
The present invention relates to computer controlled fiber placement machines which apply fiber tows to construct components. More particularly, the present invention relates to maintaining alignment of the fiber tows as they progress between a fiber supply and a tool which moves about under computer program control to apply the fiber tows.
II. Description of the Prior Art
By way of background, a computer controlled fiber placement machine includes a creel assembly which feeds a band of individual fiber tows under tension to a tool such as a fiber placement head. The fiber placement head is mounted to a robot wrist, for example, and is thus movable under program control through a wide variety of spatial orientations. As the fiber placement head moves about, fiber tows are applied to a mandrel, for example, to construct a component such as an air foil. Typically, the creel assembly is spaced from the fiber placement head, thus allowing for substantial movement of the fiber placement head relative the creel assembly. As the fiber placement head moves in a wide variety of patterns relative the creel assembly, however, the band of fiber tows therebetween will twist and bend. To this end, the band of tows may be threaded about a pair of redirect rollers which guide the band between the creel assembly and the fiber placement head, the redirect rollers being adapted to swivel about an axis perpendicular their rotational axes so that as the fiber placement head moves, tension on the tows will cause the redirect rollers to swivel in a manner tending to maintain the fiber tows in alignment and reduce the likelihood of damage to the tows.
If the tension on the tows is relatively low, or if the tow pregs are tacky, however, one or both of the redirect rollers may not swivel sufficiently, in which event the fiber tows may be damaged or the machine shut down. For example, if there is insufficient swivel of the redirect rollers, one or more of the tows may rub against each other or the edges of a roller, or may even come away from a roller altogether.